Most of the commercially available merchandise as a softener composition for fibers are compositions comprising a quaternary ammonium salt containing two long-chain alkyl groups in one molecule and being typified by a di(long-chain alkyl) dimethyl ammonium chloride. However, the quaternary ammonium salt suffers from the problem that, when residues thereof after treatment is discharged into the environment such as a river, most of them are accumulated without biodegradation.
As improved products against this problem, N-methyl-N,N-bis(long-chain alkanoyl oxyethyl)-N-(2-hydroxyethyl) ammonium methyl sulfate etc. are commercially available. The product is produced by esterification of triethanolamine with a long-chain fatty acid and then quaternizing with dimethyl sulfate. The reaction molar ratio of the fatty acid to triethanolamine is usually from 1.8 to 2.1, and, at the same time, the ratio of the amount of the diester quaternary salt to the total amounts of the monoester, diester and triester quaternary salts is from 43 to 47% by weight. It has been considered that the reaction molar ratio was made in the range of 1.8 to 2.1 because the proportion of the diester quaternary salt is maximized in this range, while the proportion of the diester quaternary salt is reduced when the reaction molar ratio is less than 1.8 or more than 2.1, so that a softening performance is reduced. However, even if the reaction molar ratio is in the range of 1.8 to 2.1, a softening effect cannot be sufficiently satisfied.
As means to solve this problem, WO97/42279 discloses a quaternary ammonium salt wherein the amount of diester quaternary salt is greater than 55% by weight, as well as it also discloses a process for producing the same. This material has improved a softening performance but is still not satisfactory. Then, WO97/42279, U.S. Pat. No. 5,916,863, U.S. Pat. No. 6,004,913 and U.S. Pat. No. 6,037,315 disclose a textile softening composition which comprises a quaternary ammonium salt which comprises a mixture of mono-, di- and tri- ester components, wherein the amount of the diester quaternary is greater than about 55% by weight. The textile softening composition may have a solvent such as water.
EP-A 675941 discloses dispersions containing a quaternary ammonium compounds which are derived from triethanolamine and which contain one, two or three fatty acyloxyethyl groups, characterized in that the percentage content of compounds containing two fatty acid acyloxyethyl groups is greater than 50 mole-%, based on the total quantity of quaternary ammonium compounds.